95' Mercury Sable 3.0w/overdrive auto trans when car reaches operating temp trans will shift fine until it shifts for third or o/d then completely disengages will not reengage until car slows and down shifts to lower gear if you accelerate for higher gear u end up disengaged again

Not supposed to shift into overdrive until the engine is warmed up and trans fluid reaches a certain temp. Accelerating in overdrive on a cold engine or cold transmission results in high emissions. so they lock it out until temps increae

too heavy a motor oil can cause hard shifting also,but when its cold out let your car warm up longer before you take off,it might help

Might need a good tranny flush my wife hauls us mail we tried a sable and tranny went in three months but with no center console there nice

Solenoid coil warms up and dissipates too much voltage with age and needs replacing. Bottom of overdrive unit. Sometimes cleaning and adjusting can help extend their life a bit.

get it to your local trans shop for a diagnostic, sounds like rebuild time.

How many miles and how does your transmission fluid look?

Get car ot normal oper. temps and put on level ground. Put trans thru all gears with foot on brake. Put into park, leave running and check level. If level is low, this could be part or all of your problem. If level is fine and trans fluid is not brown or burnt, you have an electronic problem.

If fluid checks ok, let me know if you have a Check engine light on, ABS light, etc.

Hope that helps.

Most likely your shift cable (from the selector to the transmission) is worn, maybe needs lubrication. Mine had a similiar problem, but had to shift it into neutral and back up to get it in reverse. A new shift cable solved the problem.

How do you know it's getting hot ? What is the Temp gauge showing ? Do the cooling fans work ? Have it checked for trouble codes an scan data checked .
It was however the correct thing to do in changing the fluid and filter - that's the first suspect. No no it wasn't , the correct thing would be to take it to a qualified repair shop . Hooking up a professional type scan tool an viewing data , inputs to transmission control module , ECM/PCM - engine computer etc. The control module controls shift solenoids -which shift the transmission . You could have 1-2 shift solenoid shorting when getting hot . View scan data is the only way to see this problem .

You are going to need the transmission rebuilt.

i had the same problem after spending $500.00 for toyota to look at it they didnt fix it and suggested i it was the auto trans and i should get it overhauled costing thousands. i didnt believe them and started to do some of my own research into the problem. the coolant temp sensor at the rear of the intake manifold tells the ecu when the engine is at correct operating temp then allows the auto trans shift into overdrive. to rule out any problems with the auto trans i disconnected the plug to the temp sensor and went for a drive when the engine was cold and it shifted straight away into overdrive no problems. you can't leave this disconnected because the engine is hard to start when cold as the temp sensor also tells the ecu that it is cold and allows the cold start injector to inject more fuel into the engine on cold start up.to overcome this i cut the wire to the sensor plug and installed a switch which i installed into the centre console.now i start the car flick the swith use overdrive then swith back to normal after car has warmed up . engine fault light appers on dash when switched on but doesnt matter. i have had this modification for 2 years now no problems.